The present invention relates generally to dielectric filters, and, more particularly, to a dielectric block filter construction of a design which minimizes the physical dimensions thereof.
Advancements in the field of radio electronics have permitted the introduction and commercialization of an ever-increasing array of radio communication apparatus. Advancements in electronic circuitry design have also permitted increased miniaturization of the electronic circuitry comprising such radio communication apparatus. As a result, an ever-increasing array of radio communication apparatus comprised of ever-smaller electronic circuitry has permitted the radio communication apparatus to be utilized more conveniently in an increased number of applications.
A radio transceiver, such as a radiotelephone utilized in a cellular, communication system, is one example of radio communication apparatus which has been miniaturized to be conveniently utilized in an increased number of applications. Additional efforts to miniaturize further the electronic circuitry of such radio transceivers, as well as other radio communication apparatus, are being made. Such further miniaturization of the radio transceivers will further increase the convenience of utilization of such apparatus, and will permit such apparatus to be utilized in further increased numbers of applications.
Pursuant to such efforts to miniaturize further the electronic circuitry comprising radio transceivers, as well as other radio communication apparatus, size minimization of the electronic circuitry comprising such is a critical design goal during circuit design.
Dielectric block filters, comprised of a ceramic material, frequently comprise a portion of the circuitry of such radio transceivers. Such dielectric block filters are advantageously utilized for reasons of cost, simplicity of manufacture, ease of installation upon an electrical circuit board, and good filter characteristics at frequencies (typically in the megahertz and gigahertz range) at which such transceivers usually are operative.
To form a filter of a block of dielectric material, holes are bored, or otherwise formed, to extend through the dielectric block, and sidewalls defining such holes are coated with an electrically-conductive material, such as a silver-containing material. The holes formed thereby form resonators which resonate at frequencies determined by the lengths of the holes.
Typically, substantial portions of the outer surfaces of the dielectric block are similarly coated with the electrically-conductive material. Spaced-apart portions of a top surface of the dielectric block are also typically coated with the electrically-conductive material whereby such portions become capacitively coupled theretogether. The resonators, due to electromagnetic intercoupling between adjacent ones of the resonators, and the portions of the top surface of the block due to capacitive coupling, together define a filter having filter characteristics for filtering a signal applied thereto.
The precise filter characteristics of such a filter can be controlled by controlling the capacitive intercouplings (and, hence, capacitive values of the capacitive elements formed thereof) and the spacing between adjacent ones of the resonators (and, hence, inductive values of the inductive elements formed thereof).
Historically, the component value of the elements comprising such a filter, and, hence, the filter characteristics of the filter formed therefrom, have been controlled in two ways. First, the capacitive values of the capacitive elements formed upon the top surface of the dielectric block are altered, and, second, the spacings between the adjacent ones of the resonators are altered.
Alteration of the capacitive values of the capacitive elements formed upon the top surface of the dielectric block is becoming a less viable means of altering the filter characteristics of a dielectric filter as the physical dimensions of such filters are reduced. The capacitive values of such capacitive elements are dependent upon the physical dimensions of the coated areas forming such elements as well as their relative spacings therebetween. Both the physical dimensions of such coated areas and their relative spacings therebetween are reduced as the physical dimensions of such filters are reduced. As a result, the range of capacitive values of which capacitive elements formed therefrom is reduced. Accordingly, alteration of the filter characteristics of such a filter constructed in such manner has become increasingly limited.
Alteration of the spacings between adjacent ones of the resonators is becoming a less viable means for altering the filter characteristics of a dielectric filter for similar reasons. As the physical dimensions of such filters are reduced, permissible increases in spacing between adjacent ones of the resonators are reduced. As a result, the range of inductive values of which the resonators may take is reduced. Accordingly, alteration of the filter characteristics of such a filter in such manner has become increasingly limited.
Accordingly, what is needed is a dielectric filter construction, and means for making such, permitting component elements thereof to be selected over a wide range of values without requiring increase in the physical dimensions of the filter.